Patent Document 1 discloses a conventional illumination appliance. This illumination appliance is a ceiling light whose main body housing including a light source provided therein is directly fixed to an installation surface, which is an indoor ceiling surface. The light source is composed of a plurality of LEDs arranged with emission surfaces thereof facing downward. The main body housing is covered on its lower side opposite to the installation surface with a transmissive cover that diffusely transmits therethrough emission light from the light source. The transmissive cover is formed to be so curved that an outer peripheral portion thereof descends with respect to a center portion thereof and to have a peripheral surface that is a cylindrical surface perpendicular to the installation surface.
Light emitted from the light source, which has become incident on an inner surface of the transmissive cover at a small incidence angle, is diffusely transmitted through the transmissive cover. As a result, uniform illumination light is emitted downward through the transmissive cover, and thus an indoor environment or the like is illuminated. Furthermore, light emitted from the light source, which has become incident on the inner surface of the transmissive cover at a large incidence angle, is reflected off the transmissive cover and then is emitted upward through the peripheral surface of the transmissive cover.
Illumination appliances of the type directly fixed to an installation surface are configured so that, by illuminating the installation surface to make it bright, they are capable of lessening an impression that a room as a whole is dark. To this end, illumination light is emitted upward through the peripheral surface of the transmissive cover so that the installation surface on which the illumination appliance is installed can be illuminated therewith.